Combination spark plug and electrical element



COMBINATION SPARK PLUGYAND ELECTRICAL ELEMENT Filed Jan. 12, 1960 Dec.12, 196 1 B. H. MARKS ETAL o 2 o n! I 5 4 5 4 1 1 1 1 17 1 1 1 1 1 1 12:22: WN UW \\\M 1 1 1 1 1 1 2727 119 1 1 1 111 1 m 1 4 10 .1 1 4 4 .4 81 Q W 1111 5 5 4 k 1 4 4 IO 2 7 2 2 O 6 Mo. 3 M 2 o 2 o O 4 3 1o x 1 1 15 I 2 1/1/12, 1 1 1 1 1 1 1 1 11 111 1 1 1 11 I I 1 1 1 1 1 10 1 1 /1 11 1 1111/ 11 1 1 3 1 11 1 1 /1./1// l/ 11/1 3 Q 1 o/ 2 8 2 3 0 4INVENTORS U ATTORNEY United States Patent 3,013,181 CGMETNATEON S?ARKPLUG AND ELECTRICAL ELEMENT Bert H. Marks and Leonard J. Sperry,Milwaukee, Wis,

assignors to Globe-Union inc Milwaukee, Wis, a corporation or" DelawareFiled .lan. 12, 196i), Ser. No. 1,903 6 Claims. ($1. SIS-58) Thisinvention relates to spark plugs which incorporate within their bodieselectric circuit elements, and particularly to such plugs which areessentially no larger than a conventional spark plug and the electriccircuit element incorporated therein limits the current passing throughthe center electrode to adapt the plugs for use in a distributorlessignition system.

In a distributorless ignition system where a single power supply iscontinuously connected to a multiplicity of spark plugs it is necessaryto provide current limiting condensers or resistors or inductors inseries with each plug to cause all the plugs to spark simultaneously asstated in United States Patent No. 2,866,839 and No. 2,866,447. Thesecurrent limiting electric circuit elements have been connected in theelectrical circuit unshielded and physically separated from the sparkplugs and have consequently been subjected to severe moisture,temperature and vibration conditions. There has also resulted increasedradio interference, excessive power loss, spark-over, susceptibility tobreakage, and impractical usage of space.

One object of this invention is to eliminate or minimize the harmfuleffects of moisture, temperature and vibration encountered by existingsystems in which separate electrical circuit elements are used incircuit with the spark plugs and to reduce the bulk of such systems.

A further object is to insulatively mount an electrical circuit elementwithin a spark plug in a manner which prevents spark-over, excessivepower loss, and susceptibility to breakage.

These objects are accomplished by mounting the electrical circuitelement in a space within the ceramic insulator of a spark plug or byusing such insulator as an integral part or such element. Thus theinsulator provides protection and physical support for the element, andspace requirements are minimized. The element may be cushioned withinthe insulator by an insulating and shock absorbing material to protectit from moisture, vibration and bad effects of temperature. In case theelement is a capacitor, voltage breakdown can be lessened by utilizingpart or" the insulator as the dielectric. However, by mounting aunitized capacitor entirely within the spark plug insulator theinsulating material will provide adequate voltage breakdown andspark-over protection from electrode to electrode of'the capacitor.

Other objects and advantages will be pointed out in or be apparent fromthe specification and claims, as will obvious modifications of the fourembodiments shown in the drawings of which:

FIG. 1 is a partial sectional view of a spark plug embodying the presentinvention;

FIG. 2 is a sectional view showing another embodiment of the presentinvention;

FIG. 3 is a sectional view showing a third embodiment of this inventionin which a portion of the insulator is not shown;

FIG. 4 is a sectional view of a fourth embodiment of the presentinvention. 1

The thicknesses of all metalized coatings, silvered surfaces, andbonding pastes are exaggerated in the drawings for the sake of clarity.

Referring to the drawings, FIG. 1 shows the preferred embodiment of thisinvention in which the center elecextends into the first counterbore 14-to retain electrode 13 in place. Powdered conductive glass 15 is placedin first counterbore 14 and an electrically conductive shank 22 havinghead 24 is pro-pressed into the glass powder. Insulator 10 is thenheated to around l500 Fahrenheit and the shank is pressed inwardly tofirmly seat shank head 24 on a tapered shoulder 25 in the insulator.This provides a hermetic seal between the center electrode and theinsulator.

A metal shell 26 is then applied to the insulator in a conventionalmanner and a ground electrode 27 is properly gapped from the centerelectrode 18.

After the metal shell is applied to the insulator capacitor unitindicated generally at 28 is mounted in counterbore 16. This unitincludes a high-K ceramic slug 30 having silvered ends or electrodes 32and 34. This capacitor is relatively small; about 0.250 inch in diameterand 0.400 inch in length. It may have a rating of from 10 to 50 m.1n.f.A thin copper ribbon 36 is soldered to end 32, and a flat headed screw38 is soldered to end 34. Screw 38 is screwed into the head of shank 22which is drilled, countersunk and tapped to receive it. The ribbonprojects beyond the end of the insulator 10. The space in counterbore 16around the capacitor unit is filled with a high voltage insulatingmaterial to prevent spark-over along the sides of ceramic slug 30 andalong the counterbore wall. A material found highly desirable for thispurpose is a mixture of silicone oil and uncured silicone rubber. Thismixture is a fairly thin liquid which is poured into counterbore 16. Thespark plug is then heated to cure the silicone material into a resilientrubber capable of withstanding the high temperatures and voltagesencountered in the spark plug stern. Better bonding of the siliconerubber to the bore and ceramic slug walls is secured if a suitableprimer wetting agent is used to coat these walls before pouring thesilicone mixture into counterbore 16.

After the rubber is cured, a terminal unit is bonded to the insulatorstem by adhesive 31. This uni-t comprises a cap 29 having a centralopening and a threaded terminal 33 having a bore 39. This terminal issecured to the cap with the opening and central bore ali ned so thatwhen the unit is placed over the end of the insulator the conductiveribbon 36 is threaded through'the terminal. Ribbon 36-is then solderedat 53' to terminal 33 and cut 011, i A

' scribed permits the relative motion between the component parts of thespark plug, caused by the different co efiicients of expansion of thevarious components, to occur without damaging the connection betweenterminal 33 and capacitor unit 28.

the resilient insulating material. The capacitor being mounted withinthe insulator and hermetically sealed will not be affected by moisture.

Spark-over along the outside of insulator 10 is prevented by providingan indentation 35 in the insulator in which silicone rubberwashers 37are mounted.

The center electrode assembly shown in FIG. 2 is constructed similarlyto that shown in FIG. 1. T he insulator the glass powder. Thesecomponents are then heated as I Connectionof capacitor unit 28 toterminal 33 as de- The stresses ordinarily caused by vibration andrelative motion of the parts are relieved by previously described toseat the head of the stud 48 on the shoulder between the first andsecond counterbores. A ceramic slug 4-2 with silvered ends or electrodes44 and 46, substantially identical with ceramic slug 36, has its end 46secured to headed stud 48 by conductive paste or by soldering and itsother end 44 is secured directly to a threaded terminal 52 by conductivepaste 5!) or the like. Finely ground mica is compacted around slug 42and the head of terminal 52 and dried. A fluorchemical is then appliedto saturate the mica thereby providing a good high voltage insulatingmaterial indicated as The center electrode assembly is next placed in avacuum and an epoxy seal 56 is made between the terminal 52 and theinsulator 47 thereby preventing the ingress of air inside the insulatorand also supporting the terminal. Epoxy resin and silicone material arealso good high voltage insulators and may be substituted for the micaand fiuorchemical mixture 54.

A capacitor may also be built into the center electrode assembly byusing the insulator itself as the dielectric of the capacitor. In FIG. 3the insulator 60 has a bore 61, a first counterbore 63 and a secondcounterbore 65. An internal electrode 62 is bonded to the inner side ofthe wall of the second counterbore 65 and an external electrode 58 isbonded to the outside of such wall opposite the inner electrode. Acenter electrode 67 is secured in bore 61 and a headed stud 64 is sealedin conductive glass 66 in the manner heretofore described; the head ofstud 64 being in good electrical contact with the electrode 62. A cap 68with a threaded terminal '70 secured thereto fits over the end of theinsulator and is soldered to the electrode 58 to form a seal and aconductive contact therewith. A protective insulating glaze 72 coverselectrode 58 thereby protecting it from deleterious forces andpreventing fiashover to the metal shell in which the assembly ismounted. In order to provide sufiicient capacity, the spark pluginsulator 60 must be longer than that used in conventional spark plugs.The increased length is also necessary to provide enough space betweencap 68 and electrode 62 to prevent spark-over. This spacing may beminimized by using insulating material 76 between the cap and electrode62.

In FIG. 4 a center electrode assembly is shown in which the dielectricof the capacitor also is formed by the insulator. In this modification atwo-piece insulator is used which provides an end wall as an additionaldielectric thereby cutting down on the required length ofthe insulatorand lessening the chances of spark-over. The insulator consists of a toppiece 86 open at only the lower end and a bottom piece 90. The inside ofpiece 86 including its end wall 88 has a metalized coating or electrode'73. The outside of piece 86 including its end wall has a metalizedcoating or electrode 82. An insulative coating 8%) is applied overelectrode 82 to prevent spark-over along the outside of the insulatorstem. The bottom piece 90 of the insulator has a boss 94- which projectsinto the 4. open lower end of top piece 86. This piece has a bore 91 inwhich a headed center electrode 92 is sealed with its head projectingfrom the boss 94 and engaging the electrode 78 when the pieces areassembled as shown.

This construction permits reduction of the length of the insulator toapproximately that of a conventional spark plug due to the increasedcapacity secured from top end 88. A cap 8-!- with a terminal fits overthe end of the insulator and is soldered to the electrode 32. Howeverthe end wall 88 completely insulates cap 84 from electrode 78 therebyeliminating the spark-over problem.

Although but tour embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

We claim:

1. A spark plug comprising: an insulator having a bore; a centerelectrode mounted in said bore; a ground electrode gapped from saidcenter electrode; a terminal supported by said insulator; an electricalelement connected between said terminal and said center electrode; aresilient high voltage insulating material surrounding said elementthereby isolating it from said insulator to prevent voltage breakdownand protecting said element against vibration and moisture.

2. The combination according to claim 1 in which said material comprisesmica saturated with a fluorchemical.

3. The combination according to claim 1 in which said material comprisescured silicone rubber.

4. A spark plug comprising: a metal shell having a ground electrode; aninsulator having a bore mounted in said shell; a center electrodemounted in said bore and gapped from said ground electrode; a ceramicslug in said bore havin capacitor electrodes on opposite ends; one ofsaid electrodes being connected to said center electrode; a conductiveribbon connected to the other of said electrodes; a terminal mounted onsaid insulator and connected to said ribbon; and resilient high voltageinsulating material around said slug.

5. The spark plug according to claim 4 in which said terminal has acentral bore, said ribbon passing through said central bore andconductively connected to said terminal at the top end thereof. 6. Thespark plug according to claim 4 in which said first mentioned capacitorelectrode is connected to said center electrode by a threaded screwsecured to said electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,164,082 Gallant Dec. 14, 1915 1,477,119 Graf Dec. 11, 1923 2,516,754Cipriani et al July 25, 1950 2,913,608 Fisher Nov. 17, 1959

